Insufficient intake of minerals has been pointed out in recent years as one cause pertaining to disease prevention and health maintenance of the human body. In this context, there is ongoing research and analysis devoted to elucidating the roles of various minerals. Among these minerals, about 70% of iron in the human body is present in heme iron of oxygen-transporting hemoglobin. When iron is insufficient, the amount of hemoglobin decreases and oxygen carrying capacity decreases accordingly, whereupon anemia develops. Iron deficiency such as anemia affect about 2 billion people in the entire population. Iron deficiency is found to give rise not only to the onset of anemia but also, among others, to the birth of low-weight infants from pregnant women, as well as to abnormal behavior and developmental delays in children. Oral supplementation of iron is a known treatment method for such diseases.
Internal absorption of orally ingested iron takes place in the form of absorption of divalent iron ions (Fe2+) in the duodenum. Foodstuffs and drugs for alleviating or healing iron deficiency disorders have been developed with the above mechanism in mind. For instance, products are provided in which iron preparations are blended into soft drinks, powdered milk, supplements, drugs and the like. Iron preparations that are used include preparations having soluble iron salts or water-insoluble iron salts as a main component, with soluble salts being widely used in particular. However, soluble iron salts have a strong iron taste, and thus are problematic, in oral use from the viewpoint of palatability. Moreover, soluble iron salts have problematic side effects derived from intrusion of ionized iron into the stomach wall. In consequence, insoluble iron salts have come to be used in recent years, with ferric pyrophosphate drawing substantial attention among such insoluble iron salts.
The iron dissolving effect in the stomach and the duodenum has a bearing on iron absorbability. If it were possible to increase dissolving of iron in the duodenum, through decrease of dissolving in the stomach, then bioabsorbability could be conceivably enhanced thanks to the resulting increase in dissolving at the duodenum. In contrast to soluble iron salts, moreover, it is found that insoluble iron salts allow alleviating or preventing the problem of stomach invasion. On the other hand, insoluble iron salts such as ferric pyrophosphate have poor iron solubility and exhibit accordingly low bioabsorbability, despite being comparatively little prone to causing disorders in the stomach. In order to solve these problems, chelate iron formulations have been developed in which for instance ferric pyrophosphate is solubilized. However, the occurrence of iron dissolving in the stomach might be a cause of vomiting, diarrhea and anorexia. Accordingly, various improved technologies have been proposed which pertain to iron preparations that contain ferric pyrophosphate.
As one such iron preparation, a ferric pyrophosphate formulation has been proposed in which microparticles of ferric pyrophosphate are prepared through addition of a dispersant to ferric pyrophosphate used for instance as a food additive; as a result, dispersibility is enhanced, and the flavor of iron is reduced thereby (Patent Document 1).
Also known are iron-reinforced milk beverages in which secondary aggregation during storage is prevented effectively through addition of sodium caseinate to microparticulate ferric pyrophosphate (Patent Document 2).
Soluble ferric pyrophosphate has also been proposed embodied in the form of a mixture resulting from blending sodium pyrophosphate, sodium citrate and the like, in order to increase the solubility of ferric pyrophosphate (Patent Document 3, paragraph [0016]).
Other research works pertaining to the bioabsorbability of ferric pyrophosphate have been reported in the literature. These include for instance evaluation of the bioabsorbability of ferric pyrophosphate with modified loss on ignition (Non-patent Document 1), evaluation of the bioabsorbability of ferric pyrophosphate with a modified average particle size (Non-patent Document 2), and evaluation of the bioabsorbability of soluble ferric pyrophosphate (Non-patent Document 3).